The rain stopped, tennis resumed, but tempers still flared as one showcourt was shut down indefinitely at the chaotic U.S. Open yesterday, leading to sweeping changes for the rest of the tournament’s schedule.

Player unrest caused the USTA to push back the men’s final from Sunday to Monday for the fourth straight year and have the women’s final take the Sept. 11 10th anniversary Sunday stage. There was also plenty of talk from the top players about forming a union to achieve better representation.

The women’s semifinals will now take place in prime time tomorrow night instead of today.

In one of the wackier days in Open history, Armstrong Stadium — the second-largest court — was closed off indefinitely because of a breach in the court caused by August’s historic rainfall that caused water to bubble up to the surface at one baseline.

According to a USTA source, Armstrong was repaired after a full day of work but will not be used today to let the fix settle in.

Andy Roddick’s fourth-round four-set victory against No. 5 seed David Ferrer was moved to the miniature Court 13, which holds a capacity of 883 seats and was overstuffed with fans.

After two days of rain wiping out the cards, all four fourth-round men’s matches were completed yesterday, with two Americans — Roddick and John Isner — moving on to today’s quarterfinals. The other American, Donald Young, was ousted by Andy Murray in straight sets.

It’s the first time two American men have made the quarters since 2008, and they will be underdogs today when Roddick faces defending champion Rafael Nadal and Isner takes on No. 4 Murray, which begins the day’s schedule at noon. It is Isner’s first quarterfinal appearance.

Tomorrow’s women’s final four has been set with the glamour match, Serena Williams facing No. 1 seed Caroline Wozniacki and Aussie Samantha Stosur battling Angelique Kerber.

With Nadal lashing out again and Roddick tearing into a prominent USTA referee on camera and in front of a few hundred fans because of the problems at Armstrong, the USTA decided to play it safe and not have half of the men’s draw play four straight days and the women three straight days.

On Wednesday, the Open tournament director Jim Curley said he still planned to keep the two finals intact as long as yesterday’s schedule was completed, and it was. (The women’s final has been played on Saturday night).

However, The Post has learned Curley changed his tune after meeting yesterday with ATP men’s director Adam Helfant and WTA director Stacey Allaster. When CBS was accommodating with the switch, it was a done deal.

“Everybody’s initial desire was to get tournament through on time,” USTA spokesman Chris Widmaier told The Post. “Looking at the total circumstances, we thought the fairest thing for players and ticket holders would be to extend the tournament until Monday. There’s a lot of moving pieces.”

Nadal leads the series against Roddick, 6-3, winning four of the last five matches. And the Spaniard clearly has his motor revved after ripping the USTA on Wednesday for caring more about money than safety and going at it again yesterday about needing to play four straight days to make the finals.

“That’s not fair,” Nadal said. “Our part of the draw will be in a very difficult situation for the player in the final. If you don’t have rest you have a big chance not to be enough fit to play well the next match.”

Despite the stretch of four straight years Monday finals, the USTA is not in discussions to add a retractable roof.

Roddick had dreamed of playing a men’s final on the 10th anniversary of 9/11, saying he had never been more proud to be an American on that day. Unfortunately, Roddick was the ugly American early yesterday.

After returning to Armstrong after the 70-minute delay, he saw a water spot and ripped into tournament referee Brian Earley.

“Why did you bring us out here? I’m really starting to get [ticked] off,” Roddick said on the court. “I was perfect the first time I came out here. How hard is it not to see water? I told you not to dab it every 30 seconds. Now I’m [ticked] off. Why are we out here right now? … I’m baffled right now, absolutely baffled.”

As he stormed off the court, Roddick was booed by a couple of hundred fans, with one yelling, “Andy, you’re a jerk.”

According to tennis sources, Roddick’s behavior is nothing unusual, as he’s known to berate public relations officials and USTA officials. In fact, one PR employee once resigned soon after a Roddick tongue-lashing.

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For today’s men’s quarterfinals, tickets from Wednesday’s canceled night session will be honored.